21003021 has 24 divisors (see below), whose sum is σ = 33054840. Its totient is φ = 12773376.

The previous prime is 21003011. The next prime is 21003053. The reversal of 21003021 is 12030012.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 1022121 + 19980900 = 1011^2 + 4470^2 .

It is not a de Polignac number, because 21003021 - 2⁶ = 21002957 is a prime.

It is a super-2 number, since 2×21003021² = 882253782252882, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a junction number, because it is equal to n+sod(n) for n = 21002994 and 21003012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21003001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 9405 + ... + 11421.

It is an arithmetic number, because the mean of its divisors is an integer number (1377285).

Almost surely, 2^21003021 is an apocalyptic number.

It is an amenable number.

21003021 is a deficient number, since it is larger than the sum of its proper divisors (12051819).

21003021 is a wasteful number, since it uses less digits than its factorization.

21003021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2125 (or 2122 counting only the distinct ones).

The product of its (nonzero) digits is 12, while the sum is 9.

The square root of 21003021 is about 4582.9053012254. The cubic root of 21003021 is about 275.9056467021.

Adding to 21003021 its reverse (12030012), we get a palindrome (33033033).

The spelling of 21003021 in words is "twenty-one million, three thousand, twenty-one".